This is really rough.
Democracy doesn't work in tribal societies.
Would confederacy?
The key: multicameral bodies which check/balance each other, with authority to execute decisions and to govern at various levels from village to state.
No nations. Just autonomous scalar regions of confederate governance.
More detail later, input welcome...
You know, on a related note, I've often wondered why the US, when establishing new governements, doesn't push for a federal or confederate system as opposed to a European (parlimentary) system. The only answer that I can really come up with is this: a leader separate from the majority ruling party, can lead all too quickly to a populist dictator. However, parlimentary set ups, I feel, don't take large ethnic divides into account. Then you end up with a government like the one in India, with too many parties to count and the need for constantly shifting alliances.
I'm afraid that is also what you'd get on a tribal level with this. But, a confederate system... I LIKE IT!